The present invention relates to a phase shifter and related application thereof, and more particularly, to a reflection-type phase shifter having a coupler with at one of a through port and a coupled port being connected to a transmission line, and a phased-array receiver or transmitter having the reflection-type phase shifter implemented therein.
Phase shifters are common components employed in a variety of wireless communication applications. For example, a phased-array receiver requires phase shifters to achieve desired beamforming. Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional reflection-type phase shifter. The conventional reflection-type phase shifter 100 includes a quadrature coupler 102 and a plurality of capacitors 104, 106. As shown in FIG. 1, the quadrature coupler 102 includes an input port Pl, a through port (direct port) P2, a coupled port P3, and an isolated port (output port) P4. The quadrature coupler 102 is also called 90-degree hybrid coupler used for dividing an input signal into two signals with 90 degrees out of phase. In addition, the power of the input signal is also split exactly in half (−3 dB) by the conventional quadrature coupler 102. When the input signal is represented by: α1=1∠0°, a first fraction of the input signal at the through port P2 is represented by:
            b      ⁢                          ⁢      2        =                            1                      2                          ⁢        ∠            -              90        ⁢        °              ,and a second fraction of the input signal at the coupled port P3 is represented by:
      b    ⁢                  ⁢    3    =                    1                  2                    ⁢      ∠        -          180      ⁢              °        .            
In general, the loads viewed by the signals b2 and b3 are matched to each other, and have the same reflection coefficient Γ being a complex number having a magnitude component and a phase component in a polar representation. As shown in FIG. 1, the capacitors 104 and 106 both act as reflection loads with an equivalent impedance
  1      j    ⁢                  ⁢    ω    ⁢                  ⁢    C  respectively viewed by the signal b2 and b3, where C is the capacitance of the capacitors 104 and 106. The signals respectively reflected (i.e., designated by Γ) from the loads (i.e., the capacitors 104 and 106) are represented by:
      a    ⁢                  ⁢    2    =                              Γ                      2                          ⁢        ∠            -              90        ⁢        °        ⁢                                  ⁢        and        ⁢                                  ⁢        a        ⁢                                  ⁢        3              =                            Γ                      2                          ⁢        ∠            -              180        ⁢                  °          .                    The reflected signals a2 and a3 are then combined out of phase at the input port P1 (i.e.,
                    b        ⁢                                  ⁢        1            =                                                  Γ              2                        ⁢            ∠0°                    +                                    Γ              2                        ⁢            ∠                    -                      180            ⁢            °                          =        0              )    ,resulting in no reflected signal output from the input port P1. However, the reflected signals a2 and a3 are combined in phase at the isolated port P4 (i.e.,
                    b        ⁢                                  ⁢        4            =                                                  Γ              2                        ⁢            ∠90°                    +                                    Γ              2                        ⁢            ∠90°                          ≠        0              )    ,resulting in an output signal b4 induced at the isolated port P4. The reflection-type phase shifter 100 therefore can be used to provide a desired phase shift by properly tuning the capacitance of the implemented capacitors 104 and 106 that changes the reflection coefficient Γ which is a complex number. For example, if the capacitance of the capacitors 104, 106 is changed from zero fF (open) to infinite fF (short), 180 degree phase shift can be achieved.
As mentioned above, the reflection loads determine the reflection coefficient Γ which controls the final phase shift of the output signal generated from the reflection-type phase shifter. Therefore, an easy and efficient means to tune the reflection load for changing the reflection coefficient to a desired value is needed.